The field of invention relates generally to optical communication systems; and in particular but not exclusively, relates to holographic optical elements for use in optical communication systems.
With increasing popularity of wide area networks such as the Internet and/or World Wide Web, network growth and traffic have experienced tremendous growth. Network users continue to desire faster networks, which may be difficult to achieve using existing wired technologies.
An alternative to wired network solutions is a wireless or free space optical (FSO) communication technology. Such FSO systems can use beams of light, such as laser beams, as optical communication signals, and therefore do not require cables or fibers connected between transmitters and receivers.
FSO units (i.e., FSO transmitters, receivers, and transceivers) used in FSO communication systems typically include several separate optical elements for transmission, reception, tracking and acquisition of FSO signals. For example, some FSO units have multiple apertures, each having a lens. Other FSO units may have a single aperture with a lens and multiple beam splitters. Because these optical elements are relatively expensive, the cost of such a unit increases as more optical elements are incorporated into the unit. Further, these optical elements typically require relatively complex mechanisms to provide needed optical isolation between elements, which further increases costs (including design costs). In addition, as more optical elements are used in a unit, alignment and maintenance of the unit becomes more complex, thereby increasing costs and the xe2x80x9cdowntimexe2x80x9d in maintaining the unit. Such increased costs and downtime are undesirable in many applications.
FSO Terminals may employ pointing and tracking systems to maintain alignment of the FSO link. The intent of these pointing and tracking systems is to optimize the optical power conveyed between the FSO terminals. There are many types of pointing and tracking systems. All of these systems require hardware additional to the communication channel in the FSO terminal. This additional hardware for a pointing and tracking system can also increase costs.
In accordance with aspects of the present invention, a FSO receiver of a FSO communication system is provided. The FSO receiver is arranged to receive a FSO signal from a FSO transmitter. In one aspect of the present invention, the FSO receiver includes an illumination sensing unit used in deriving alignment information from portion(s) of the FSO signal incident on illumination apertures of the FSO receiver. The FSO receiver provides this information to the FSO transmitter. The FSO transmitter uses the information to adjust it pointing direction (i.e., the direction that it transmits FSO signals).
In another aspect, the illumination apertures are formed in a holographic optical element (HOE) having apertures for other features of the FSO receiver. For example, the HOE may also include reception and tracking apertures. In some embodiments, the FSO receiver in incorporated in a transceiver. In such embodiments, the HOE can also include a transmission aperture (which may include component apertures).
In yet another aspect, the multiple apertures are formed in a single substrate of the HOE. This aspect can advantageously reduce the complexity and cost of the optics unit used in the FSO receiver.